Hydraulic positive displacement rotary machines



Se t. 7, 1965 D. FIRTH ETAL 3,204,569

HYDRAULIC POSITIVE DISPLACEMENT ROTARY MACHINES 3 Sheets-Sheet 1 Filed March 1, 1963 N hx Sept. 7, 1965 D. FIRTH ETAL I HYDRAULIC POSITIVE DISPLACEMENT ROTARY MACHINES Filed March 1, 1963 3 Sheets-Sheet 2 HYDRAULIC POSITIVE DISPLACEMENT ROTARY MACHINES Filed March 1, 1965 Sept. 7, 1965 D. FIRTH ETAL 3 Sheets-Sheet 3 United States Patent 3,204,569 HYDRAUMC POSlTliVlE DESPLACEMENT RQTARY MACHINES Donald Firth and Roger Harvey Yorke Hancock, East Kilhride, Glasgow, Scotland, assignors to Council for Scientific and Industrial Research, London, England, a body incorporated under the laws of the United Kingdom Filed Mar. 1, 1963, Ser. No. 262,109 Claims priority, appiication Great Britain, Mar. 9, 1962, 9,279/62 2 Claims. ((ll. 103162) This invention relates to hydraulic positive displacement rotary machines of the kind (hereinafter referred to as the kind described) in which a cylinder block which is rotatable relative to a cam member and a port member has a plurality of cylinders containing pistons reciprocable under the control of the cam member and ports communicating with the cylinders, each port being arranged to communicate in the course of said rotation alternately with inlet and outlet ports in the port member.

The invention is particularly but not exclusively applicable to swash plate hydraulic machines in which a cylinder block having a plurality of cylinders lying generally parallel to the axis of rotation of the block, is rotatable between a stationary back plate or port block and a non-rotatable swash plate, the latter usually being adjustable for inclination of its plane in order to vary the stroke of the pistons in the cylinder block in accordance with the demands of the system to which the machine is coupled.

The smooth and quiet operation of machines of the kind described, especially at relatively high line pressures, is largely determined by the timing of the port events for each cylinder. As each cylinder comes into communication with a high pressure or a low pressure port, there is a risk of the setting up of a shock wave in the hydraulic fluid at the instant of each new registration as a result of the fluid in the cylinder being at a substantially diiferent pressure from the pressure of the fluid in the inlet or outlet port. For example, a cylinder moving into communication with the outlet port may contain fluid at substantially the same pressure as exists in the inlet port. The shock waves not only cause noise in the hydraulic circuit but also impose shock loads on both the cylinder block and port member of the machine and the equipment associated with the hydraulic circuit.

In order to overcome this difliculty, it has already been proposed, in UK. patent specification Nos. 893,848 and 934,851, to interpose an angularly adjustable port plate between the working surface of the cylinder block and the port block of a swash plate machine. This port plate has arcuate ports of generally similar angular extent to those in the port block and in register therewith, and means is provided for angularly adjusting this port plate so as to change the angular positions of register of each cylinder with the arcuate ports in the port plate. This enables each piston to be displaced within its cylinder to compress or decompress oil therein before the cylinder is exposed to the next port pressure. For example, when a cylinder is transferring from register with a low pressure port into register with a high pressure port, the above-mentioned adjustment can be made so that the piston begins to compress the oil trapped therein while the cylinder is still blanked off by the space between the adjacent ends of the two arcuate ports. This precompression of the cylinder charge should, theoretically, continue until the oil pressure is equal to that in the high pressure port. No shock Wave is then set up in the oil in the cylinder or the port at the instant of commencement of register between the two. These earlier proposals have the disadvantage that changes in the timing 3,Z4,569 Patented Sept. 7, 1965 ice of cylinder opening and changes in the timing of cylinder closing always accompany each other, whereby the effi ciency of the machine is impaired under many operating conditions. It is an object of the the present invention to provide means by which the disadvantage of the earlier proposals can be avoided.

The invention provides a hydraulic positive displacement rotary machine of the kind referred to wherein a control member which is angularly adjustable about the axis of rotation is disposed between the cylinder block and the port member and has inlet and outlet ports through which the cylinder block ports can communicate with the ports in the port member, the port member and the control member being adapted to cooperate so that said angular adjustment varies the lengths of are for which each cylinder block port communicates with the ports in the port member while one end of each of said lengths of are is at a point fixed with respect to the port member. The angle of rotation during which each cylinder is sealed before communicating with an inlet or outlet port thus starts or finishes at a point fixed relative to the port member and can be varied as desired by adjustment of the control member.

In one construction in accordance with the invention, a projection may be provided at one end of each of the port member inlet and outlet ports, said projection being a sliding fit in the associated port in the control member and a least substantially filling the radial cross-sectional area of said control member port. Thus, adjustment of the control member varies the length of the portions of the control member port on opposite sides of the projection and, since the portion overlapping the port member is sealed off from the other portion by the projection, the effective length of the control member port (i.e. the length communicating with the port in the port member) is varied.

The simplest form of projection is a cylindrical stud fixed in the port member just beyond one end of the port-or, if preferred, arranged to define one end of the port. The projection must, of course, not stand proud of the surface of the port member so as to foul the cylinder block.

The following is a description, by way of example, of an embodiment of the invention, as applied to a swash plate machine (described in detail for use as a pump, but also capable of use as a motor), reference being made to the accompanying drawings in which:

FIGURE 1 is an axial cross-section of the complete pump assembly,

FIGURE 2 is an elevation of the discharge end of the pump, and

FIGURE 3 is an elevation of an arrangement of port plate and port block in accordance with the present invention for the pump shown in FIGURES 1 and 2.

The pump illustrated consists of a main frame or body having a front end plate I and a ported back end plate or port block 2 clamped by four pillars 3. Each end plate 1, 2 carries a journal bearing 4, 5 respectively for a short rigid drive shaft 6. Adjacent the bearing 5 in the back end plate 2, the shaft 6 is formed with a locking taper section '7 on which is looked a cylinder block 8. This block is drawn up on the taper by a back-nut 9 on the shaft. The cylinder block 8 contains a number of cylin ders l-tl whose axes are mutually inclined inwards towards the back end plate 2. A piston 11 in each cylinder is reciprocable under the control of a normally fixed swash plate 12 carried on trunnions. The swash plate 12 has a central conical aperture 14 through which the shaft 6 passes, the dimensions of this aperture being sufficient to allow for adjustment of the angle of the swash plate to the shaft 6.

The Working face of the swash plate is recessed t0 accommodate an annular bearing pad and an annular slipper plate 16. The latter is free to rotate under the frictional drag of slippers 17 each of which is engaged with a respective piston 11. For clarity of illustration in FIGURE 1, only one cylinder 1t), piston El. and slipper 17 is shown.

The back face 18 of the cylinder block 8 is pierced by inlet/outlet ducts or ports 19, one to each cylinder 10, the openin s to which register successively with arcuate inlet and outlet ports 2%), 21 respectively in a floating port plate 22. This port plate is not anchored to the back end plate 2 except for angular orientation about the shaft 6 with respect to the swash plate 12. This angular orientation is controlled by means of a threaded rod 23 which is slidable in a bore 24 in the back end plate 2 and which engages, at its inner end, a locating peg 25 fastened to the port plate 22 and projecting into the bore 24. The rod 23 is axially adjustable by means of a captive capstan nut 26. The ports 20, 21 communicate with an external circuit by way of flared ducts 27, 28 respectively and inlet and outlet sockets 27a, 28a in the back end plate 2. The ducts 27, 2% open through a bearing surface 29 on the back end plate in the form of two arcuate ports registering with the arcuate ports 20, 21 respectively in the port plate 22.

The port plate 22 forms a kind of washer between the mutually opposed faces 18 of the cylinder block 8 and 29 of the back end plate 2, and has a limited freedom to float radially between the two. This radial floating action is hydrostatically controlled by means of internal ducts and cavities. The port plate 22 also has leakage oil layers between its flat faces and the opposed faces 18 and 29 giving substantially equal and opposite axial loadings on the port plate and thus has a limited freedom to float axially. The pump as illustrated in FIGURES l and 2 is described in greater detail in our UK. patent specification No. 893,848.

Referring now to the arrangement shown in FIGURE 3, into each arcuate port 20, 21 of the port plate 22 projects a pin 30, 31 respectively, each pin being carried by the port block 2 and defining the adjacent end of the corresponding port in the port block. Each pin is a sliding fit in its arcuate port 20 or 21 and completely occupies or substantially completely occupies the depth of the port (i.e. the thickness of the port plate 22). Thus, each pin occupies the radial cross-sectional area of the port and the flow of fluid past the sides or end of the pin is substantially prevented, while angular adjustment of the port plate is still possible. As shown in the drawing, the ports 20, 21 extend angularly beyond the pins 30, 31 by 6, leaving a blanked-off pocket 32 which does not communicate with either port in the port block. Thus, whenever a cylinder comes into register with this pocket 32, there is no significant change in the cylinder contentsi.e. the oil already in the cylinder remains trapped.

The distance 33 measured along the arcuate axis of the two ports 26, 21 represents the blanked-off zone of travel of each cylinder between the ports, during which time the piston is passing beyond either top or bottom dead centre. The distance 33 is a minimum when 0 is zero, and in this position of the port plate 22 the opposite ends of the ports 20, 21 register substantially with the corresponding ends (indicated in broken lines) of the ports 20, 21, in the port block.

Assuming that the cylinder block is rotating clockwise, as shown by the arrow R, then, since the port 20 is the inlet port of the pump, the pin defines the end of each inlet stroke, when the piston passes through top dead centre on the axis OO, after which point compression of the oil commences. The further each cylinder has to travel before it commences to register with the port 21, the higher is the pro-compression of the oil before dis charge through the outlet port 21 begins. The angle 0 is thus chosen so that the pre-compression pressure is substantially equal to the discharge line pressure in the outlet port 21. The same sequence, in respect of de compression occurs as each cylinder moves from register with the outlet port 21 at bottom dead centre on the axis 0-0 to register with the inlet port. The more accurately these pressures are matched, the smoother and quieter the machine operates.

If the machine is working at full load, the port plate is adjusted for maximum retard of the next port event, i.e., a a and this allows maximum compression or decompression of the oil trapped in the cylinder at the end of the induction or discharge stroke, respectively, so that the pressure in a cylinder is brought to substantially the discharge or inlet pressure, as the case may be,

efore the next port event.

It will be noted that the trailing end of each port 20, 21 is fixedly defined by the respective pins 3%, 31, so that the instant of cut-off of each cylinder as it leaves each port is not varied by angular adjustment of the port plate. The machine is thus a uni-directional machine.

Instead of being circular in cross-section, each pin 30, 31 may be elongated in the direction of the common arcuate axis of the ports 20, 21 and its outer and inner flanks shaped to the same curvature as the radially outer and inner walls of the respective ports so as to provide an extended seal against the port Walls. Furthermore, the side of each pin which faces along its respective port may be machined radial to the port plate, or concave to the port.

As will be understood, the need for angular adjustment of the port plate 22 to equalise cylinder and port pressures does not only arise when there are fluctuations in line pressure, but also when the stroke of the pistons is changed by changes in the angle of inclination of the swash plate. The latter has the effect of varying the rate of change of cylinder pressure with angle of rotation, and hence the angular position of the port plate 22 should be made a function of both line pressure and swash plate inclination.

The machine shown in FIGURES 1 and 2 can be used as a hydraulic motor as well as a pump. In the case of a motor, pressure fluid must be supplied to each cylinder as its piston moves from bottom dead centre to top dead centre and each cylinder must be connected to exhaust as its piston moves from top dead centre to bottom dead centre. It is therefore desirable to seal off the cylinder as it approaches top dead centre and bottom dead centre so that oil therein is pre-decompressed before the cylinder communicates with exhaust and pro-compressed before the cylinder communicates with the pressure source. Consequently, when the machine is used as a motor, pressure oil is supplied to port 21 and port 20' is connected to exhaust. As a result the cylinder block rotates anti-clockwise, in the opposite direction to the arrow R, and the arrangement of FIGURE 3 is operable to adjust the degree of precompression and pre-decompression of the oil in each cylinder before it reaches bottom dead centre and top dead centre respectively.

We claim:

1. A hydraulic positive displacement rotary machine comprising a cam member, a port member, a cylinder block rotatable relative to the cam member and port member, a plurality of cylinders in the cylinder block, pistons reciprocable in said cylinders under the control of the cam member, a control member disposed between the cylinder block and the port member, registering inlet and outlet ports in the control member and port member, ports in the clyinder block communicating with said cylinders and opening through a face of the cylinder block directed towards said control member, each of said cylinder block ports alternately communicating with the inlet and outlet ports in the port member through the inlet and outlet ports in the control member when said relative rotation occurs, adjustment means for adjusting the angular position of the control member about the axis of rotation, said inlet and outlet ports in the control member and port member having end portions adapted to overlap in a circumferential direction, a first projection on the port member at one end of the inlet port therein, and a second projection on the port member at one end of the outlet port therein, each said projection being a sliding fit in the associated port in the control member and at least substantially filling the radial cross-sectional area of said contnol member port whereby one end of the efi'ective arcuate length of each of the control member inlet and outlet ports is at a point fixed with respect to the port member and said effective arcuate lengths are varied by said adjustment of the control member.

2. A swash plate hydraulic machine comprising a swash plate, a port block, a rotatable cylinder block, a plurality of cylinders in the cylinder block, pistons recip-- rocable in the cylinder block under the action of the swash plate, a port plate disposed between the cylinder block and the port block, registering arcuate inlet and outlet ports in the port plate and port block, ports in the cylinder block communicating with said cylinders and opening through a face of the cylinder block directed towards the port plate, said port plate ports and cylinder block ports being at the same radius from the axis of rotation, a first projection on the port block at one end of the inlet port therein and a second projection on the port block at one end of the outlet port therein, each said projection fitting into and filling the radial crosssection of a port in the port plate, and adjustment means for adjusting the angular position of the port plate about the axis of rotation.

References Cited by the Examiner UNITED STATES PATENTS 2,546,583 3/51 Born 103-462 FOREIGN PATENTS 1,247,031 10/60 France.

DONLEY I. STOCKING, Primary Examiner.

LAURENCE V. EFNER, Examiner. 

1. A HYDRAULIC POSITIVE DISPLACEMENT ROTARY MACHINE COMPRISING A CAM MEMBER, A PORT MEMBER, A CYLINDER BLOCK ROTATABLE RELATIVE TO THE CAM MEMBER AND PORT MEMBER, A PLURALITY OF CYLINDERS IN THE CYLINDER BLOCK, PISTONS RECIPROCABLE IN SAID CYLINDERS UNDER THE CONTROL OF THE CAM MEMBER, A CONTROL MEMBER DISPOSED BETWEEN THE CYLINDER BLOCK AND THE PORT MEMBER, REGISTERING INLET AND OUTLET PORTS IN THE CONTROL MEMBER AND PORT MEMBER, PORTS IN THE CYLINDER BLOCK COMMUNICATING WITH SAID CYLINDERS AND OPENING THROUGH A FACE OF THE CYLINDER BLOCK DIRECTED TOWARDS SAID CONTROL MEMBER, EACH OF SAID CYLINDER BLOCK PORTS ALTERNATELY COMMUNICATING WITH THE INLET AND OUTLET PORTS IN THE PORT MEMBER THROUGH THE INLET AND OUTLET PORTS IN THE CONTROL MEMBER WHEN SAID RELATIE ROTATION OCCURS, ADJUSTMENT MEANS FOR ADJUSTING THE ANGULAR POSITION OF THE CONTROL MEMBER ABOUT THE AXIS OF ROTATION, SAID INLET AND OUTLET PORTS IN THE CONTROL MEMBER AND PORT MEMBER HAVING END PORTIONS ADAPTED TO OVERLAP IN A CIRCUMFERENTIAL DIRECTION, A FIRST PROJECTION ON THE PORT MEMBER AT ONE END OF THE INLET PORT THEREIN, AND A SECOND PROJECTION ON THE PORT MEMBER AT ONE END OF THE OUTLET PORT THEREIN, EACH SAID PROJECTION BEING A SLIDING FIT IN THE ASSOCIATED ORT IN THE CONTROL MEMBER AND AT LEAST SUBSTANTIALLY FILLING THE RADIAL CROSS-SECTIONAL AREA OF SAID CONTROL MEMBER PORT WHEREBY ONE END OF THE EFFECTIVE ARCUATE LENGTH OF EACH OF THE CONTROL MEMBER INLET AND OUTLET PORTS IS AT A POINT FIXED WITH RESPECT TO THE PORT MEMBER AND SAID EFFECTIVE ARCUATE LENGTHS ARE VARIED BY SAID ADJUSTMENT OF THE CONTROL MEMBER. 